1. Field of the Invention
The present invention concerns a toner for electrostatic image development used upon developing electrostatic latent images formed by an electrophotographic method, an electrostatic recording method or the like, and a manufacturing method thereof, as well as an electrostatic image developer and an image forming method.
2. Description of the Related Art
A method of visualizing image information by way of electrostatic imaging such as an electrophotographic method has now been used in various fields. In the electrophotographic method, an electrostatic image is formed on a photoreceptor in the steps of charging and exposing, then developing the electrostatic latent image with a developer containing a toner, and thus visualizing the image in the steps of transferring and fixing.
As the developer used in the method, there have been known a two-component developer comprising a toner and a carrier, and a single-component developer comprising either one of a magnetic toner and a non-magnetic toner. As a manufacturing method for the toner, generally used is a kneading pulverization method in which a thermoplastic resin is melted and kneaded together with a pigment, a charge controller or a releasing agent such as wax, then after cooling, finely pulverized and classified. According to the method, a toner being excellent to a considerable degree can be produced. However, there are some problems such as decline in developing properties due to a stress in a developing device or the like, degradation of image quality, and contamination of other components, which may be attributed to the indefinite shape of the toner, generation of fine powder, tendency of the releasing agent to be exposed on the surface of the recording medium.
Further, to meet the increasing demand for higher image quality, and especially in formation of a color image, the toner has been remarkably miniaturized to achieve higher image fineness. Further, in a case of a digital full-color copier or printer, a color image is formed by color-separating the original color image using filters of B (blue), R (red) and G (green), then developing latent images that correspond to the original image having a dot diameter of 20 to 70 μm with developers of Y (yellow), M (magenta), C (cyan) and BK (black), in accordance with a subtractive color process. Thus, a great amount of a developer has to be transferred as compared with a conventional black-and-white machine in such cases. Therefore, the importance of uniform chargeability, durability, toner intensity, and sharpness in particle size distribution has also been increasing to respond to a small dot diameter.
On the other hand, importance of improvement in glossiness has also been growing to meet the demand for improvement in quality of a full-color image in copiers and printers. Proposals have thus been made to improve glossiness while ensuring offset resistance. Further, there has also been proposed an invention intended not merely for improvement in glossiness but also improvement in image quality by eliminating gloss unevenness.
However, it is required for a high-grade full-color image to achieve not only favorable glossiness but also favorable fine line reproducibility at the same time. Particularly, requirement for a high-grade full-color image has been increasing in a case of using a thick paper sheet such as a poster board, where compatibility between high glossiness and fine line reproducibility is difficult to achieve and gloss unevenness tends to occur in half-tone reproduction at the time of fixation, due to low heat conductivity of a thick paper sheet.
As described above, difficulty in achieving high glossiness without causing gloss unevenness and improved fine line reproducibility at the same time, only based on the toner techniques described above, has been increasing.